1. Field of the Invention
The present invention relates to a method for processing a substrate in which occurrence of defects after ion implantation can be suitably prevented, for example, in a Si semiconductor substrate.
2. Description of the Prior Art
In the field of manufacturing Si semiconductors, recently, SOI (Silicon on Insulator) technique capable of providing a high-speed, low-power consumption LSI is advancingly developed, and SIMOX (Separation by Implanted Oxygen) has attracted attention as a method for manufacturing a wafer necessary for this.
According to this method, oxygen atom ion O.sup.+ is implanted to a Si wafer 20 heated to 500-650.degree. C. by ion implantation in the order of 10.sup.17 -10.sup.18 /cm.sup.2 as shown in FIG. 2(a). The accelerating voltage in this ion implantation is set to about 200 kV, whereby the oxygen ion is dosed to the area of several 10 to several 100 nm from the surface (hereinafter referred to as a dosing area 21).
A heating treatment to a temperature equal to or higher than 1300.degree. C. for 6-10 hours (high-temperature annealing) is successively performed in an inert gas such as Ar or an mixture gas of Ar and oxygen added thereto. The oxygen atom implanted to the dosing area 21 is reacted with Si by this annealing to form a buried oxide film 22 formed of silicon dioxide (SiO.sub.2) having a substantially uniform thickness in a specified depth from the surface as shown in FIG. 2(b).
By use of a substrate having the buried oxide film 22 thus formed thereon (hereinafter referred to as a SIMOX substrate 20'), a device formation is performed in a Si layer 23 of 10-500 nm on the surface side from the buried oxide film 22, or the part insulated from a Si base layer 24 on the lower side by the buried oxide film 22 to form an element, whereby a high-speed, low-power consumption LSI can be manufactured.
However, the conventional SIMOX substrate 20' formed according to the above method has a problem in that defects as reduce the manufacturing yield or reliability can not be sufficiently reduced in the manufacture of an ULSI (IC with ultra-high integration degree) in which integration of elements is further advanced.
Namely, in the above-described manufacturing process, in the substrate 20 after ion implantation, crystal defects such as atomic vacancies Dv . . . in the surface Si layer 23, substitutional lattice defects Dc . . . in which O atom is substituted by Si atom, interstitial lattice detects Di . . . in which O atom is penetrated between atoms, and the like occur in large quantities according to the ion implantation as shown in FIG. 2(c). The high-temperature annealing after ion implantation leads to a behavior as these crystal defects are mutually integrated, resulting in a change to defects of a larger level as large vacancies PV (Piled up Vacancies), stacking fault SF, or dislocation DF as shown in FIG. 2(d), and these are existing in the SIMOX substrate 20'. Further, the buried oxide film 22 is not necessarily a chemically stable SiO.sub.2 layer.
Although it is conventionally adapted to change the temperature, time, temperature rising speed or the like in the annealing in order to reduce such defects, dislocation of a high density in the order of 10.sup.9 /cm.sup.2 still remains in a high dose substrate having a dose of about 2.times.10.sup.18 /cm.sup.2. It is also reported that the dislocation density can be significantly reduced by changing the dose of oxygen ion to about 4.times.10.sup.17 /cm.sup.2. However, it is the actual state that the dislocation density is about 10.sup.2 /cm.sup.2 even in that case, which is still insufficient to be applied to ULSI.